This invention relates to a process for the preparation of hexagonal plate-like .alpha.-Fe.sub.2 O.sub.3, a material commonly called Micaceous Iron Oxide and abbreviated to MIO, which is of use as an important material for paints and high grade ferrites.
Typical examples of known processes for the preparation of MIO are described in Japanese Patent Applications Publication Nos. 43(1968)-12435 and 48(1973)-29718. In these processes usually ferrous sulfate formed as a by-product in the preparation of titanium oxide, or ferrous sulfate or ferrous chloride resulting from pickling of steel is utilized as the starting material, and MIO is prepared by first oxidizing the employed iron salt by using an oxidizer such as nitric acid or a chlorate and, after neutralization, performing a hydrothermal treatment in an aqueous alkali solution. These processes have attracted attention because of the possibility of preparing MIO from abundantly wasted iron salts which are liable to become origins of environmental pollution, but from an economical viewpoint these processes cannot be asserted to be very profitable because the most expensive material among the raw materials for the preparation of MIO is alkali, not iron source.